Project Summary Posttranslational modifications (PTMs) regulate protein functions and play ubiquitous roles in a wide and diverse range of cellular processes in eukaryotes. Not surprisingly pathogens have evolved to target eukaryotic PTMs for promoting bacterial infection. Ubiquitination is a PTM that regulates multiple cellular processes including immunity, vesicle trafficking, and cell cycle control. Chlamydia trachomatis targets PTMs by secreting the virulence factor ChlaDUB1, which functions as a deubiquitinating and deneddylating enzyme. Preliminary studies indicate that ChlaDUB1 acts early in infection to attenuate activation of the NF-kB pathway while in mid stages of infection ChlaDUB1 targets host PTMs for co-opting cellular organelles. We hypothesize that C. trachomatis uses ChlaDUB1 to counteract host immune defenses and to exploit host resources. To test this hypothesis, genetically engineered C. trachomatis strains will be generated to dissect the PTM activities of ChlaDUB1 and to define their roles in manipulating NF-kB signaling and host organelles. The impact of these activities on C. trachomatis replication and the immune responses elicited will be assessed in in-vivo models of infection. Secondly, through a series of biochemical analyses and proteomic approaches designed to quantitatively measure global changes to host PTMs, substrates targeted by ChlaDUB1 during dampening of NF-kB activation and co-option of organelles will be identified.